Alkylation of heptanes with isobutane using antimony pentafluoride-fluorosulfonic acid mixtures

ABSTRACT

A HYDROCARBON CONVERSION PROCESS INVOLVING ALKYLATION AND DISPROPORTIONATION OF LOW OCTANE C7 ALKANE STREAMS IN THE PRESENCE OF ISOBUTANE TO FORM HIGHER OCTANE MIXTURES OF PREDOMINATLY SATURATED HYDROCARBONS, SAID PROCESS UTILIZING A MIXTURE OF FLUOROSULFONIC ACID AND ANTIMONY PENTAFLUORIDE AS A CATALYST.

IJune 25, 1974 D, A, MCCAULAY 3,819,743

EPTANES WITH 1s Usme ANTmoNY MIXTUR'ES ALKYLATION OF H OBUTANE LUOROSULFONIC ACID PENTAFLURIDE-F Filed Dec. L5, 1972 United States PatentOHce 3,819,743- Patented June 25, 1974 U.S. Cl. Mtl-683.47 4 Claims ABSTRACT OF THE DISCLOSURE A hydrocarbon conversion process involving alkylation and dsproportionation of low octane C., alkane streams in the presence of isobutane to form higher octane mixtures of predominantly saturated hydrocarbons, said process utilizing a mixture of fluorosulfonic acid and antimony pentauoride as a catalyst.

SUMMARY OF THE INVENTION This invention relates to a novel process for producing a high octane hydrocarbon mixture from a low octane C7 hydrocarbon stream and, more specifically, to an alkylation-disproportionation process for octane upgrading of a heptane stream using a system comprised of a low octane heptane feed, an isobutane feed and a catalyst which is a mixture of iluorosulfonic acid and antimony pentafluoride.

In accordance with the instant invention, a low octane heptane feed (low octane heptane being used here in the sense of any feed which is composed predominantly of one or more low octane C, saturated hydrocarbons such as n-heptane or the methyl hexanes) is dispropqrtionated and alkylated in the presence of a branched satu'rated hydrocarbon, isobutane, by a mixture of tluorosulfonic acid and antimony pentatluoride to yield a product stream which is predominantly a mixture of high octane alkanes. This process may be carried out at about atmospheric pressure and below ambient temperatures.

BACKGROUND OF THE INVENTION One of the major problems in petroleum refining is the production of low octane hydrocarbon streams during the refining process. These low octane streams must then be converted to mixtures of hydrocarbons having a higher octane number. Various techniques have been developed for this purpose including alkylation, isomerization, disproportionation and various combinations of these individual techniques. Various catalysts have been used for the accomplishment of alkylation, isomerization and disproportionation among which are Friedel-Crafts type of catalyst including hydrogen fluoride-boron triuoride mixtures and the so-called super acids such as uorosulfonic acid-antimony pentauoridc mixtures. However, no good processes for handling C7 streams have been developed. The instant invention is directed to an improved alkylation-disproportionation procedure by which higher octane mixtures of hydrocarbons can be formed from C7 streams than has been heretofore accomplished. Using the instant invention, for example, a normal heptane feed treated with a uorosulfonic acid-antimony pentafluoride mixture in the presence of isobutane is disproportionated and alkylated and the pentanes, hexanes and heptanes formed are substantially at their isomeric equilibria in which isopentane, dimethylbutanes and, for the heptanes, dimethylpentanes and triptane predominate.

BRIEF DESCRIPTION OF THE DRAWINGS The Figure shows a ow diagram for one mode of carrying out the instant invention.

STATEMENT OF THE INVENTION An embodiment of the instant invention is illustrated in the flow diagram of the Figure. A C, cut of light naphtha, preferably after drying, dearomatization and desulfurization to reduce catalyst poisoning, is mixed with isobutane and introduced through line 1 into stirred reactor 2. The isobutane to C7 feed weight ratio is maintained between about 0.1 to about 5, more preferably, between about 0.5 to about 2 and, most preferably, between about 0.8 to about 1.2.

In reactor 2 the feed is stirred with liquid catalyst entering through line 3. Make-up catalyst enters through line 4 and consists of a mixture of 0.1 to about 2.0 volumes, more preferably, about 0.2 to about 1.2 and, most preferably, about 0.5 to about 1.0 volumes of antimony pentauoride per volume of uorosulfonic acid. Preferably, as high a purity of uorosulfonic acid and antimony pentauoride as is economically feasible is used, and special precautions should be used to keep these catalyst components as dry as possible prior to and during use.

The temperature in reactor 2 is kept between about 20 F. and about 70 F., more preferably, between about 0 F. and about 40 F. and, most preferably, between about 10 F. and about 30 F. Advantageously, the entire process of the instant invention is run at or near atmospheric pressure.

Space velocities are important for achieving maximum octane upgrading and depend upon reactor temperature and a lower space velocity will naturally be used at a lower reaction temperature. It has been found that at about 70 F. space velocities between about 0.5 to about 3.0 volumes of feed per volume of catalyst per hour into the reactor are useful. At about 20 F. a space velocity between about 0.01 to about 0.05 volumes of feed per volume of catalyst per hour is used and, at about 14 F. a space velocity between about 0.10 to about 0.15 volumes of feed per volume of catalyst per hour is employed. Catalyst is used throughout to mean a mixture of fluorosulfonic acid and antimony pentauoride.

The reactor etlluent is passed into settler 5 where the catalyst phase separates as a bottom layer and is recycled to reactor 2 through line 6. A slip stream of catalyst is taken olf via line 7 for catalyst rejuvenation. In the catalyst regeneration zone 8 residual catalyst is separated from red-oil and various other reaction products. If desired, these other reaction products may be treated to recover for reuse a substantial part of their tluorine and antimony.

The hydrocarbon product is taken from settler 5 through line 9 into column 10. Here the isobutane which is unreacted is distilled overhead and returned through line 11 to the reactor. The debutanized gasoline at the bottom of column 10 is removed through line 12 and sent to storage.

Comparison of Example I, heptanes isomerized without isobutane using an antimony pentauoride-uorosulfonic acid mixture, and Example II, heptanes treated by the instant invention, shows that when isobutane is added (l) less acid soluble oil is formed (a measure of catalyst degradation), (2) about twice as much C5 and C8 products are produced, and (3) more of the higher octane isomers in the C5, C6 and C, fractions are pro' duced.

While the invention is described in connection with the specific Examples below, it is to be understood that these are for illustrative purposes only. Many alternatives, modifications and variations will be apparent to those skilled in the art in the light of the below Examples and such alternatives, modifications and variations will fall within the Scope and spirit of the appended claims.

3 GENERAL PROCEDURE For the runs made in Examples I and II below a mixture of 8 milliliters of antimony pentafluoride, 25 milliliters of uorosulfonic acid and 225 milliliters of heptane was stirred at ,-10" C. Samples of the hydrocarbon product were withdrawn at intervals for analysis and analyzed using vapor phase chromatography.

EXAMPLE I Feed composition, (weight percent):

Isobutane- Heptanes 100 Contact time, (hours) i 17 Product composition (weight percent): l 7 3 4 21s 3317 0.0 17. 4 0.1 21.4 p 95.4 9.1 Acid-soluble oil 1. 0 15. 0 Pentane isomer distribution, (weight percent):

Isopentane 91. 1 n-Pentane 8. 9 Hexane isomer distribution (weight percent):

Dimethylbutanes- 68. 6 Other 31.4 Heptane isomer distribution (weight percent):

Dimethylpentanes 55. 2 Triptane 13.2 Other 31.6

EXAMPLE II Feed composition (weight percent) isobutane 50.7 Heptanes 43.9 Contact time (hours) 48 Product composition (weight percent) Propane l1.8 Butanes 43.9 Pentanes 19.8 Hexanes 22.5 Heptanes 12.1 Acid-soluble oil 1.0 Pentane isomer distribution (weight percent) Isopentane l 89.7 n-Pentane 10.3 Hexane isomer distribution (weight percent) Dimethylbutanes 77.1 Other 22.9 Heptane isomer distribution (weight percent) 'Dimethylpentanes 76.8 Triptane 5.7 Other 17.5

What is claimed is:

1. A process for upgrading the octane rating of a hydrocarbon feed which is a low octane heptane or a low octane mixture which is substantially composed of heptanes comprising:

(a) contacting said low octane heptane or said low octane mixture which is substantially composed of heptanes with isobutane in the presence of a uorosulfonic acid-antimony pentauoride catalyst at a temperature between about 20 F. and about F., and

(b) separating a mixture of higher Octane hydrocarbons from the combination of step (a).

2. 'Ihe process of Claim 1 wherein step (a) is carried out between about 0 F. and about 40 F.

3. A continuous process for upgrading the octane rating of a hydrocarbon feed which is a low octane heptane or a low octane mixture which is substantially composed of heptanes comprising? (a) contacting said low octane heptane or said low octane mixture which is substantially composed of heptanes with isobutane in the presence of a uorosulfonic acid-antimony pentauoride catalyst at a temperature between about -20 F. and about 70 F., and

(b) separating a mixture of higher octane hydrocarbons from the combination of step (a), and

(c) recyclingthe uorosulfonic acid-antimony pentauoride catalyst to step (a), and

(d) separating unreacted isobutane from said mixture o'fhigher octane hydrocarbons and recycling said isobutane to step (a).

4. The process of Claim 3 wherein step (a) is carried out between about 10" F. and about 30 F. and at a space velocity of between about 0.05 volumes of said feed per volume of said catalyst to 'about 0.2 'volumes 0f said feed per volumes of said catalyst.

References Cited UNITED STATES PATENTS 3,636,129 1/ 1972 Parker et al. 26o- 683.47 3,708,553 1/ 1973 Olah 26o-683.47

G. J. CRASA-NAKIS, Assistant Examiner D. E. GANTZ, Primary Examiner U.S. Cl. X.R. 260-683.58, 676 

